lesson
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If you pour fruity squash into an ice-lolly mould and put it in the freezer, it comes out as a crunchy, solid treat. How does runny juice turn into hard ice?
Taking Away Heat
Liquids can flow and change shape, but solids keep their own shape. When you put a liquid in a cold place, heat escapes from the liquid into the cold air around it.
📊Interactive diagram
Does a liquid need to be inside a kitchen freezer to turn solid?
Freezing and Solidifying
When a liquid cools down and turns into a firm solid, we say it freezes or solidifies. Both words describe the exact same change of state.
Pure water freezes into solid ice when it cools down to 0 °C. But runny candle wax solidifies on your table at room temperature, while melted rock cools into solid stone at over 700 °C!
📊Interactive diagram
People often think 'freezing' only means icy cold because of water. In science, even glowing lava is freezing when it hardens into rock as it cools!
Once a liquid has frozen solid, is it stuck that way forever?
A Reversible Change
If you leave your ice lolly out in the sunshine, it takes in heat and melts back into runny juice. No new material was made — it is still the same squash!